(Oprah.com) -- If you heard there was a weapon proven to prevent most crimes before they happen, would you run out and buy it? World-renowned security expert Gavin de Becker says this weapon exists, but you already have it. He calls it "the gift of fear."

One chapter in Gavin's book "The Gift of Fear" has stuck with Oprah since she first read it.

The story of a woman named Kelly begins with a simple warning sign. A man offers to help carry her groceries into her apartment -- and instantly, Kelly doesn't like the sound of his voice. Kelly goes against her gut and lets him help her -- and in doing so, she lets a rapist into her home.

"We get a signal prior to violence," Gavin says. "There are preincident indicators. Things that happen before violence occurs."

Gavin says that unlike any other living creature, humans will sense danger yet still walk right into it.

"You're in a hallway waiting for an elevator late at night. Elevator door opens, and there's a guy inside, and he makes you afraid. You don't know why, you don't know what it is. Some memory of this building -- whatever it may be. And many women will stand there and look at that guy and say, 'Oh, I don't want to think like that. I don't want to be the kind of person who lets the door close in his face. I've got to be nice. I don't want him to think I'm not nice.' And so human beings will get into a steel soundproof chamber with someone they're afraid of, and there's not another animal in nature that would even consider it."

For weeks, Nicole had a funny feeling that something odd was going on in her apartment. "My gut started feeling like something just wasn't right," she says. "I would come home, and there would be just weird lights on in my house -- lights that I didn't even remember turning on in the first place."

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Then one day, Nicole noticed a UPS delivery box where it shouldn't be. "I'm like, 'How did this brand of box get on my back balcony?'" Nicole began to feel uneasy -- but continued to brush it off. "I would just come home, you know, and almost feel nauseous," she says. "I kept trying to justify it saying, 'Okay, it is in my head.'"

Nicole's funny feeling eventually escalated into full-fledged panic attacks, which Gavin says were her intuition's way of telling her that something was wrong.

"And intuition records everything. So when she started getting panics attacks, her intuition is saying, basically, 'You're not going to listen? Okay, I'll ramp it up. I'll give you panic attacks. You want sleepless nights? I'll give you sleepless nights.'"

Nicole eventually did listen to her intuition, starting with a simple test. "I dropped a tank top behind the door as I was leaving for work, thinking that when I come home that night, I'm going to peek my head around the corner. If [the tank top] had been pushed to the side, it would have been obvious that the door was opened." When Nicole got home, she says the tank top had moved.

Caught on camera

The next day, Nicole says she set up a hidden camera to try and find out what was going on in her apartment. Once she came home, Nicole says she plugged the camcorder into her laptop. "And the first thing I see is this man's head peeking around the corner into my house," she says. "What I felt at that point was just complete terror. I'm sitting there watching this video --this story unfold -- and this person comes in my house, is looking around, going through my things, looking through my laundry, holding up my lingerie."

As Nicole continues to watch in horror, the intruder undresses himself and puts her lingerie on. "So this person is in my clothes, proceeds to start pleasuring himself -- just very, very graphic things happening right there in my house with my belongings. And he finishes up, takes off my clothes -- and puts them exactly back as I had left them -- puts his clothes back on, checks to make sure nobody's outside the door and leaves."

After watching the tape, Nicole says she ran around her apartment, screaming hysterically. She says she had never seen the man in the tape before. "Initially, I took my cell phone, called my boyfriend at the time, screaming hysterically. All I could say was, 'He's in my house. He's in my house.' Even picking up the phone, dialing, was difficult."

Two weeks later, police found the man -- 39-year-old Shawn Rogers, a computer consultant with a young son and a wife at the time. Police were unable to charge Rogers with anything more than trespassing ... until he came back to Nicole's apartment to steal her camera. Police were able to charge Rogers with burglary, and he was sentenced to eight years in prison.

Dangerous behavior

When Nicole found the UPS box on her balcony, Gavin says this was a warning sign. Gavin applauds Nicole for listening to her intuition and says that quieting her fear could have caused the situation to escalate. "He's already into behavior of wanting to get caught," he says. "You don't come back again and again and again and not want to get caught."

Gavin says like Nicole, the intruder's intuition was probably trying to tell him something too. "Offenders as well can see what's happening in their lives. And talk about not listening to it -- he's in someone's apartment doing something sexual with their clothes on -- that's something to listen to."

Because the intruder had a job and a family, Gavin says his behavior was not only reckless, but dangerous as well.

"When people do listen, they can stop what's almost fate," Gavin says. "There's a great line that Carl Jung said. He said, 'What we do not make conscious emerges later as fate.' If he made it conscious, if he could talk to someone about it, if he could tell someone, he could get better also. But he didn't, and it does mean escalation. If she discovered him, that's dangerous. If he came in when she was there, that's dangerous."

Your feelings are warnings

Doris, who says she endured years of sexual abuse at the hands of her husband, appeared on "The Oprah Show" after leaving her husband. Unfortunately, her battle didn't end there -- two months after she left him, Doris's ex-husband abducted her at gunpoint and raped her.

After the show, Oprah spoke with Doris again to ask if her she had sensed any warning signs the night she was abducted. "As I was coming home from work, it was just a very eerie, strange feeling as I drove up," Doris says. "It was darker than normal in my driveway, and there was a trash can sitting where I normally park right in the middle.

"I thought, 'Hmm, this is strange.' Because my mother lives with me, and she'll turn on the lights when it gets dark. It did give me a little eerie feeling -- the hairs on the back of your neck kind of stand up. But still, I didn't listen to my instincts."

Gavin says that "eerie feeling" is exactly what he wants women to pay attention to. "We're trying to analyze the warning signs," he says. "And what I really want to teach today and forever is the feeling is the warning sign. All the other stuff is our explanation for the feeling. Why it was this, why it was that. The feeling itself is the warning sign."